The Chicago Symphony Orchestra has just hired its first black player. You may need to rub your eyes and reread that sentence before believing that a landmark institution in one of America's great melting-pot conurbations has finally got around to lifting its tacit colour bar. However, facts are facts and who's to say that the arrival of Tage Larsen (his father was half-Norwegian) as fourth trumpet won't turn Chicago into a beacon of tolerance?

The CSO is, at any rate, no worse than its major competitors. The New York Philharmonic has one tenured black musician on its books, Boston and Cleveland two each and Philadelphia three. None of these outsiders has been promoted to a principal position. A survey by the American Symphony Orchestral League estimates black membership of its 200-odd ensembles at 1.4 per cent, and falling.

African-Americans happen to be the largest single ethnic group in Chicago - 1.05 million out of 2.9 million inhabitants, or 36.4 per cent of the population, according to the latest census. It makes you wonder how the orchestra can presume to represent the great metropolis while effectively excluding its majority community.

But let's not get too smug here. Professor Earl L Carter of the Juilliard School, who monitors black participation in concert life, assures me that there are only five black musicians in all of the UK's 12 symphony orchestras - one each in the Philharmonia, London Philharmonic, BBC Symphony, Royal Liverpool Philharmonic and City of Birmingham Symphony orchestras. Put another way, there is one black player for every 12 million British listeners.

Discriminatory as this might sound, it is not a case for the Race Relations Board or for another of those self-parodying Arts Council investigations into "Racism in Theatre" where the conclusion is written into the title before the panel is picked. This particular virus runs far deeper than race. It is endemic to every orchestra and, unless checked, will render the genre extinct.

Take the turbulent issue of sex. It is 20 years next month since Herbert von Karajan invited Sabine Meyer, a clarinettist, to join the Berlin Philharmonic, thereby breaking up one of the cosiest men-only clubs in the cosmos. The boys yelped that Meyer's tone did not match theirs and voted her out by 73 to four.

Karajan, incensed, ended his lifelong contract with Berlin. The breach embittered the rest of his life, wrecked the career of the orchestra's late manager, Peter Girth, and haunts the excellent Sabine Meyer to this day with echoes of unsought notoriety.

Berlin has since mended its ways, halfways at least. The band that Sir Simon Rattle inherits next month includes 14 women of varied nationalities. All it lacks is a single player from the eastern half of Germany. Two ex-DDR citizens did succeed in passing auditions but, after a probationary period in the orchestra, were told that they were somehow incompatible. With or without women, the Berlin Philharmonic remains socially a closed shop.

The Vienna Philharmonic, a bastion of masculine exclusivism, is about to admit the first woman member next month. Many of its players swear hand on heart that they have nothing against women; some of the ones I know seem, if anything, overfond of feminine company. Their resistance to reform stems from a patrilineal tradition, by which seats in the orchestra are passed from father to son and the sound is supposedly preserved.

Several VPO men boast descent from musicians who played under Gustav Mahler (and, they forget to add, replaced him with a balletmaster). The sonics, too, are something of a myth: the Vienna sound has thickened since the War as decibel levels rose in competition with US orchestras.

The appearance of one or two women in Vienna - it will never be more - will not jeopardise hallowed traditions any more than it has done in London orchestras, where women have played their part ever since the men marched off to die on the Somme. Yet even in London, the most egalitarian of orchestral towns, women and minorities still feel excluded from the heart of many orchestras.

No symphony orchestra in London has a woman concertmaster; the LSO tried one but she lasted less than a season. There are no women percussionists, often a gay preserve. The Philharmonia has been more welcoming to Jewish musicians than the London Philharmonic. The LSO is more open than most to Russians.

Quirks and irregularities are widely held to give symphony orchestras their corporate identity and esprit de corps. Conditions are strikingly different in smaller ensembles - the English Chamber Orchestra has a splendid leader in Stephanie Gonley - and in period-instrument bands where women players often preponderate. Intriguingly, early music audiences are holding up better than symphonic subscriptions.

The issue, as I have said, is not purely a matter of prejudice. VPO players are no more misogynist than CSO men are racist. Both bands now stage blind auditions behind a screen to ensure that an applicant is judged on ability, and not on looks or graces. Larsen won his Chicago place from a field of 100 contenders.

Social aspects have to be taken into consideration. Too few blacks can afford a tertiary musical education; too few women have been encouraged to bang a drum; too few orchestral musicians have opened their minds to the vitality of non-European cultures.

Yet, when all is said and done, there is a problem, and it lies in the very nature of the symphonic orchestra, an organism that was formed at the onset of industrial revolution and has resolutely resisted egalitarianism, electronics and multicultural values.

The symphony orchestra simply bypassed the 20th century. If it wants to survive the 21st, it will need to reform from the heart - not by admitting a token outsider or staging a free concert for the poor, but by opening itself to the spirit of the times and engaging with the things that really matter. You will know that the symphony orchestra has discovered its soul when Chicago play the Proms, all night in the park, under a West Indian music director.